December 4th, 2008
Nuclear fusion as future power source
MIT researchers have used their Alcator C-Mod fusion reactor, in operation since 1993, to bring the promise of fusion as a future power source a bit closer to reality. As you probably know, fusion is the reaction that produces the sun’s energy and it has an ‘enormous potential for future power generation because fusion plant operation produces no emissions.’ Their advances are closely scrutinized by scientists participating to the planned ITER (International Thermonuclear Experimental Reactor) now under construction in France. But read more…
You can see above the control room of the Alcator C-Mod fusion reactor where two graduate students perform experiments. (Photo credit: Paul Rivenberg, MIT) The original version of this photo was featured in a recent issue of MIT TechTalk magazine (Volume 53, Number 10, December 3, 2008) (PDF format, 7 pages, 725 KB).
These research projects have been conducted at the MIT Plasma Science & Fusion Center (PSFC), where the Alcator C-Mod project is led by Earl Marmar. “The Alcator C-Mod reactor, in operation since 1993, has the highest magnetic field and the highest plasma pressure of any fusion reactor in the world, and is the largest fusion reactor operated by any university.”
But fusion power plants are still very far away. “One of the most vexing issues facing those trying to construct a fusion plant that produces more power than it consumes (something never achieved yet experimentally) is how to propel the hot plasma (an electrically charged gas) around inside the donut-shaped reactor chamber. This is necessary to keep it from losing its heat of millions of degrees to the cooler vessel walls. Now, the MIT scientists think they may have found a way. Physicist Yijun Lin and principal research scientist John Rice have led experiments that demonstrate a very efficient method for using radio-frequency waves to push the plasma around inside the vessel, not only keeping it from losing heat to the walls but also preventing internal turbulence that can reduce the efficiency of fusion reactions.”
So what are the latest results obtained by the team? “Lin says that ’some of these results are surprising to theorists,’ and as yet there is no satisfying theoretical foundation for why it works as it does. But the experimental results so far show that the method works, which could be crucial to the success of ITER and future power-generating fusion reactors. Lack of a controllable mechanism for propelling the plasma around the reactor ‘is potentially a showstopper,’ Rice says, and the ITER team is ‘very concerned about this.’ Rice adds that ‘we’ve been looking for this effect for many years,’ trying different variations of fuel mixture, frequency of the radio waves, and other parameters. ‘Finally, the conditions were just right.’ Given that the ITER project, which will take 10 years to build, is already underway, ‘our results are just in time for this,’ Lin says.”
This research work has been published in Physical Review Letters under the title “Observation of ion cyclotron-frequency mode conversion flow drive in tokamak plasmas” (Volume 101, Number 23, Article 235002, December 5, 2008). Here is a link to one of the most obfuscated abstracts I have ever read.
Judge by yourself… “Strong toroidal flow (V
) and poloidal flow (V
) have been observed in D-3He plasmas with ion cyclotron range of frequencies (ICRF) mode-conversion (MC) heating on the Alcator C-Mod tokamak. The toroidal flow scales with the rf power Prf (up to 30 km/s per MW), and is significantly larger than that in ICRF minority heated plasmas at the same rf power or stored energy. The central V responds to Prf faster than the outer regions, and the V(r) profile is broadly peaked for r/a
0.5. Localized (0.3r/a0.5) V appears when Prf
1.5 MW and increases with power (up to 0.7 km/s per MW). The experimental evidence together with numerical wave modeling suggests a local flow drive source due to the interaction between the MC ion cyclotron wave and 3He ions.”
For easier understandable information, the same research team has published a very similar paper on November 25, 2008 on the MIT website, “Ion Cyclotron Antenna Impurity Production and Real Time Matching in Alcator C-Mod.” Here are the links to the abstract and to the full paper (PDF format, 9 pages, 287 KB).
Sources: David Chandler, MIT News Office, December 3, 2008; and various websites
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